Influence of Tectonic Movements on Hydrocarbon Accumulation in the Dongying Formation, Western Bohai Bay Basin, China

The hydrocarbon accumulation process in the Dongying Formation (a key Cenozoic reservoir in the western Bohai Bay Basin) is complex due to superimposed tectonic activities. To reconstruct its evolution, we integrated fluid inclusion analysis, burial–thermal history reconstruction, and fault–cap rock sealing evaluation. Results reveal that the Baoding Sag experienced at least two major hydrocarbon charging stages, further subdivided into four sub-periods (I–IV) based on the microthermometry and fluorescence characteristics (ranging from yellow, indicating marginal maturity, to blue, indicating maturity). The hydrocarbons exhibit a mixed composition, as reflected in the fluid inclusions and Ro evolution, indicating a complex charging history derived from two source rocks (Es1 and Es3). However, two key tectonic activities that significantly influenced the hydrocarbon accumulation process can still be distinguished: uplift erosion at 22.3 Ma and strike-slip faulting at 11.8 Ma. Specifically, the 11.8 Ma strike-slip faulting caused the leakage of early hydrocarbons (Periods I–II) from the Dongying Formation into the Guantao Formation, with a critical fault juxtaposition threshold of ~86 m. This fault activity also introduced water washing of the hydrocarbon reservoir. Later, around 0.36 Ma, gas washing occurred as the source rocks matured, further complicating the calculation of the mixing ratio between the two source rock contributions.